A wide variety of pieces of fruit and vegetable have a specific gravity that is close to that of water and usually slightly greater than that of water. Desirable and undesirable articles often have slightly different densities, and such articles have often been separated by floatation separation. In floatation separation, the articles are placed in a body of liquid such as water, and those with slightly greater specific gravity, such as the undesirable ones, sink in the water while those of slightly smaller specific gravity than the others float on the surface.
One example of such separation is in the olive industry, where a pitting tool is used to remove the pits from olives to provide pitted olives. The pit removal process sometimes fails, usually leaving a significant fragment of the pit in the olive. A major liability faced by companies selling pitted olives, is lawsuits from persons who have broken a tooth on a pit fragment remaining in a supposedly pitted olive. One technique that has been successfully used to remove pitfailed olives (those from which not all of the pit has been removed), is to float the olives in a pool of salt water. The pitfailed olive containing all or a major portion of the pit has a density of about 1.05, while a pitted olive containing only the pulp (the desirable part without the pit) has a density of about 0.99 to 1.01. The density of water can be increased to about 1.11 by increasing its salinity up to about 15%. By adding sufficient salt to fresh water to increase the density to about 1.02, the pool of salt water can be used to float those olives which have been pitted from those which have been pitfailed. The exact per cent of salt, and therefore the exact density of the salt water, is adjusted for the particular batch of olives to be floatation separated.
Environmental concerns have made it difficult for olive processors to use salt water for floatation separation. The salt water has to be frequently changed, such as every day to avoid excessive odors. The salt in the water makes it an undesirable sewer discharge, where water from the treated sewage will be reused either directly or by way of rivers or underground water. Sugar can also be added to water to increase its density, but sugar water is also an undesirable sewer discharge because it is difficult to clean. A floatation separation system for distinguishing pitted olives from pitfailed olives, which avoided the need for highly salted or sugared water, would be of considerable value. Such a floatation separation system could also be valuable in separating other pitted fruits such as cherries, as well as in separating articles of fruit or vegetables which have a specific gravity close to that of water but wherein desirable pieces have a slightly different specific gravity from undesirable ones.